Item label does not align with the widget (ALIGN_TOP vs ALIGN_CENTER_VERTICAL) with wx

It looks like with this simple example:

```python
from traits.api import HasTraits, Str
from traitsui.api import View, Group, Item

class Employee (HasTraits):
name = Str('foo')

view = View(
Group(
Item(name='name'),
orientation='vertical',
show_labels=True,
show_left=True,),
resizable=True,
height=.1)

if __name__ == '__main__':
emp = Employee()
emp.configure_traits(view=view)
```
When run with wx on Linux (GTK), it looks like the label is aligned to the top of the text box.

It seems like the code that cause this is changed to use wx.ALIGN_TOP instead of wx.ALIGN_CENTER_VERTICAL, which IMHO looks weird:

https://github.com/enthought/traitsui/blob/master/traitsui/wx/ui_panel.py#L1090

Is there any reason to do so instead of the old behavior?